What are the causes of a stroke?

Stroke occurs when a blood vessel is blocked by a clot (an ischemic stroke) or when a blood vessel in the brain ruptures (hemorrhagic stroke). Larger strokes can cause swelling and compression in the brain. In both types of stroke, the flow of oxygen-rich blood is cut off to a part of the brain and brain cells die. As a result, a person suffers neurological deficits related to the part of the brain that is damaged. Most of the 750,000 strokes that occur in the US each year are ischemic strokes (88 percent) but hemorrhagic strokes are more likely to be deadly.

Ischemic strokes are often the result of carotid artery disease, a buildup of plaque inside walls of the arteries in the neck, which can restrict or block the flow of blood to the brain. In addition, blood clots can develop on the plaque, which can break loose and block brain arteries, causing a stroke. People with high blood pressure, heart disease, diabetes, who smoke, are obese, or have a family history of the disease are at greater risk of developing carotid artery disease.

A hemorrhagic stroke occurs when a blood vessel in the brain ruptures. Most hemorrhages occur as a consequence of high blood pressure, which can lead to rupture of tiny arteries deep in the brain. In another type of hemorrhage, called subarachnoid hemorrhage, the rupture is at the site of an aneurysm, a bulge that develops in a weak area of an artery's wall. Less often the rupture occurs where there is an abnormal connection between arteries and veins (arteriovenous malformation or AVM). This congenital abnormality may be present at birth, but it is usually only identified when symptoms develop. Both aneurysms and AVMs can be surgically repaired if they are identified before a stroke occurs.

All organs and tissues in your body need a steady stream of oxygenated blood to function. If your brain does not receive the proper amount of blood, you may have a stroke. Stroke is the third highest cause of death in the United States, behind only heart disease and cancer, and is a leading cause of long-term disability. According to the American Heart Association, each year nearly 800,000 people in the United States will experience a stroke.

There are a number of causes of stroke, but the two main causes are

- Decreased blood flow to the brain from a main artery
- A blood clot or other “debris” that blocks a small blood vessel in the brain

In addition, there are many cases where the reason for a stroke is unclear. These are called cryptogenic strokes.

Strokes caused by a decrease in blood flow to the brain are called ischemic strokes. These strokes can be the result of a blockage in one of the carotid arteries or other arteries in the brain. Blockages most often occur when a fatty substance called plaque narrows the artery so much that blood cannot flow freely.

A stroke can cause brain damage and result in loss of hand, leg and voice function or even death.  

Anyone who thinks he or she is experiencing a stroke should call for an ambulance immediately. With a stroke, time lost is brain function lost, so seeking urgent medical attention is critical.

In the worst cases, stroke occurs when the flow of blood to a portion of the brain is cut off entirely, killing or damaging brain cells.

Most strokes are caused by essentially the same processes that lead to angina or heart attack -- plaque builds up in an artery in or leading to the brain, squeezing off the flow of blood. Sometimes, a clot will form in the artery, cutting off the blood flow entirely. Other times, a clot will form somewhere else in the body, then travel to the brain to lodge in an artery there.

A stroke can also occur when a diseased artery in the brain bursts, and the risk of this happening rises sharply with hypertension. When a blood vessel bursts, cells nourished by the damaged artery are deprived of blood. At the same time, blood from the hemorrhage puts pressure on the brain, impairing function.

The brain can reroute nerve impulses around damaged areas when the damage isn't too severe, to restore at least some function, but injured brain cells can't be replaced, so prevention of stroke is vital.

A stroke is caused when blood flow to a part of the brain is cut off or when there is bleeding into the brain. Strokes can cause permanent brain damage, but sometimes the damage can be stopped or reversed.

A stroke usually is caused by a blockage in the arteries that supply blood to the brain. Once the blood flow is cut off, that part of the brain starts to “suffocate” and die unless the blood flow can be restored. Blockages can be caused by blood clots that travel from other parts of the body, like the heart, or they can be caused by slow damage to the arteries over time from diseases such as high blood pressure and diabetes.